final drainage report for settlers view …...final drainage report for settlers view subdivision...

FINAL DRAINAGE REPORT

for

SETTLERS VIEW SUBDIVISION

Prepared for:

Hannigan and Associates, Inc.19360 Spring Valley Road

Monument, Colorado 80132

February 17, 2017

Prepared by:

19 E. Willamette AvenueColorado Springs, CO 80903

(719)-477-9429(719)-471-0766 faxwww.jpsengr.com

JPS Project No. 111603

dsdlaforceCalloutRename to Preliminary Drainage Report.

dsdlaforceText BoxAdd: PCD File No.: SP-17-006

dsdlaforceText Box1. Use the latest version of UD-Detention (v3.07)

2. The Stormwater Detention and Infiltration (SDI) design data sheet and EPC MS4 post construction form (attached) will be required with the final plat application.

El Paso County MS4 Post Construction Detention / Water Quality Facility Documentation Form

This document must be completed and submitted with required attachments to the County for projects requiring a detention and/or a water quality facility. A separate completed form must be submitted for each facility.

Project name:

Owner name:

Location Address:

Latitude and Longitude:

Assessor's Parcel #: Section: Township: Range:

Expected Completion date:

Project acreage: Design Ponding Acres: Design Storm:

Design Engineer Email Address:

To ensure compliance with C.R.S. 37-92-602(8), the completed Stormwater

Detention and Infiltration Design Data Sheet must be attached. The form can be found here:

https://maperture.digitaldataservices.com/gvh/?viewer=cswdif# (click on Download SDI Design Data Sheet)

List all permanent water quality control measure(s) (EDBs, rain gardens, etc):

For all projects for which the constrained redevelopment sites standard is applied, provide an explanation of why it is not practicable to meet the full design standards.

Attach Operations and Maintenance (O&M) Plan describing the operation and maintenance procedures that ensure the long-term observation, maintenance, and operation of control measure(s), including routine inspection frequencies and maintenance activities. If multiple, different water quality control measures are used at the same location, a separate O & M Plan must be provided for each facility.

Attach Private Detention Basin / Stormwater Quality Best Management Practice Maintenance Agreement and Easement addressing maintenance of BMPs that shall be binding on all subsequent owners of the permanent BMPs.

Attachments: Review Engineer

Stormwater Detention and Infiltration Design Data Sheet EPC Project File No.

O & M Plan

Maintenance and Access Agreement

August 2016

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SETTLERS VIEW SUBDIVISIONFINAL DRAINAGE REPORT

TABLE OF CONTENTSPAGE

EXECUTIVE SUMMARY...................................................................................................... i

DRAINAGE STATEMENT ....................................................................................................ii

FLOODPLAIN STATEMENT .............................................................................................. iii

I. GENERAL LOCATION AND DESCRIPTION................................................................... 1

II. DRAINAGE BASINS AND SUB-BASINS.......................................................................... 3

III. DRAINAGE DESIGN CRITERIA........................................................................................ 4

IV. DRAINAGE PLANNING FOUR STEP PROCESS............................................................. 5

V. DRAINAGE FACILITY DESIGN ........................................................................................ 5

VI. EROSION / SEDIMENT CONTROL ................................................................................. 10

VII. COST ESTIMATE AND DRAINAGE FEES..................................................................... 10

VIII. SUMMARY.......................................................................................................................... 10

APPENDICES

APPENDIX A Hydrologic CalculationsAPPENDIX B Hydraulic CalculationsAPPENDIX C Detention Pond CalculationsAPPENDIX D Detention Pond Operation & Maintenance ManualAPPENDIX E Drainage Cost Estimate

APPENDIX F FiguresFigure A1 Vicinity MapFigure FIRM Floodplain MapSheet EX1 Historic Drainage PlanSheet D1 Developed Drainage PlanSheet D1.1 Enlarged Developed Drainage PlanSheet C1 Site Grading & Erosion Control Plan

dsdlaforceCalloutExtract the O&M Manual from the drainage report. This item will be a required standalone submittal document with the final plat application.

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SETTLERS VIEW– FINAL DRAINAGE REPORTEXECUTIVE SUMMARY

A. Background

Settlers View is a proposed residential subdivision of a 40-acre parcel locatednorthwest of Hodgen Road and Steppler Road in El Paso County.

The proposed subdivision consists of 14 rural residential lots with 2.5-acreminimum lot sizes.

Settlers View is located within the East and West Cherry Creek Drainage Basins,each of which comprise total drainage areas in excess of 30 square miles. TheSettlers View property represents less than 0.2 percent of the total basin area.

B. General Drainage Concept

Developed drainage within the site will be conveyed along paved streets withroadside ditches and culverts, as well as grass-lined channels through drainageeasements, following historic drainage patterns.

Developed flows from the subdivision will be detained to historic levels throughan on-site private stormwater detention pond.

Subdivision drainage improvements will be designed and constructed to meet ElPaso County standards,

C. Drainage Impacts

The proposed detention pond will detain to historic flows at the downstreamproperty boundary, ensuring no significant adverse developed drainage impact ondownstream properties.

Drainage facilities within public road rights-of-way will be dedicated to theCounty for maintenance. The proposed stormwater detention pond will bemaintained by the subdivision HOA.

DRAINAGE STATEMENT

Engineer's Statement:

The attached drainage plan and report were prepared under my direction and supervision and arecorrect to the best of my knowledge and belief. Said drainage report has been prepared according tothe criteria established by the City/County for drainage reports and said report is in conformity withthe master plan of the drainage basin. I accept responsibility for liability caused by negligent acts,errors or omissions on my part in preparing this report.

John P. Schwab, P.E. #29891

Developer's Statement:

I, the developer have read and will comply with all of the requirements specified in this drainagereport and plan.

By:_______________________________________________________________________________Printed Name: Date

El Paso County's Statement

Filed in accordance with the requirements of the El Paso County Land Development Code,Drainage Criteria Manual, Volumes 1 and 2, and Engineering Criteria Manual as amended.

Jennifer Irvine, P.E. DateCounty Engineer / ECM Administrator

Conditions:

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FLOODPLAIN STATEMENT

To the best of my knowledge and belief, no parts of the Settlers View Subdivision are located in aFEMA designated floodplain, as shown on FIRM panel No. 08041C0325F, dated March 17, 1997.

John P. Schwab, P.E. #29891

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I. GENERAL LOCATION AND DESCRIPTION

A. Background

Settlers View is a proposed rural residential subdivision located in northeastern El Paso County,Colorado. The Settlers View parcel (El Paso County Assessor’s Number 61000-00-463) is locatedbetween Grandview Subdivision and Settlers Ranch Subdivision, west of Steppler Road, as shownin Figure A1 (Appendix F). Settlers Ranch Subdivision will consist of 14 low-density residentiallots (2.5-acre minimum size) on a 40-acre parcel. The north boundary of this site adjoins thecurrent termination of Silver Nell Drive in Grandview Subdivision.

B. Scope

This report is intended to fulfill the El Paso County requirements for a Preliminary and FinalDrainage Report (FDR) for submittal with the Preliminary Plan and Final Plat applications. Thereport provides a summary of site drainage issues impacting the proposed development,including analysis of impacts from upstream drainage areas, site-specific developed drainagepatterns, and impacts on downstream facilities. This FDR report has been prepared based on theguidelines and criteria presented in the El Paso County Drainage Criteria Manual.

C. Site Location and Description

The Settlers View parcel is located in the Northeast Quarter of Section 23, Township 11 South,Range 66 West of the 6th Principal Meridian. The site is currently a vacant meadow tract, withsome existing trees at the north end of the property.

The property is currently zoned RR-5 (Rural Residential; 5-acre minimum lots), and theproposed subdivision will include re-zoning the property to RR-2.5 (Rural Residential; 2.5-acreminimum lots). The proposed low-density lots will be served by individual wells and septicsystems.

The north boundary of the property borders the existing Grandview Subdivision, and the southboundary of the property adjoins the approved Settlers Ranch Subdivision, both of which consistprimarily of 2.5-acre lots. The west boundary of the borders an undeveloped 40-acre ranchproperty, and the east boundary of the site adjoins a currently vacant 40-acre property which isproposed for development as the Abert Ranch Subdivision, with 2.5-acre minimum lots.

Access through Settlers View Subdivision will be provided by extension of Silver Nell Drivesoutheasterly through the property, along with construction of the proposed Settlers View Roadextending southwest from Silver Nell Drive. Subdivision infrastructure improvements willinclude paving of new public roadways through the site, as well as grading, drainage, and utilityservice improvements for the proposed residential lots. Local roads will be classified as ruralminor residential roads, with 60-feet rights-of-way and paved widths of 28-feet.


Ground elevations within the parcel range from a low point of approximately 7,570 feet abovemean sea level at the west boundary of the parcel, to a high point of 7,650 feet near the northboundary.

This site is located along the ridge between the East and West Cherry Creek drainage basins.Surface drainage from the east edge of the property flows easterly towards tributaries of EastCherry Creek, and surface drainage from the western part of the site flows southwesterly towardstributaries of West Cherry Creek. The terrain is rolling with slopes ranging from 2% to 8%.Existing vegetation is typical eastern Colorado prairie grass.

D. General Soil Conditions

According to the Soil Survey of El Paso County prepared by the Soil Conservation Service, on-sitesoils are comprised of the following soil types (see Appendix A):

Type 25 – Elbeth sandy loam: Hydrologic Group B (northwest corner of site) Type 67 – Peyton sandy loam: Hydrologic Group B (east side of property) Type 92 – Tomah-Crowfoot: Hydrologic Group B (southwest part of property; majority of

site)

E. References

City of Colorado Springs & El Paso County “Drainage Criteria Manual, Volumes 1 and 2,” revisedMay, 2014.

El Paso County “Engineering Criteria Manual,” January 9, 2006.

FEMA, Flood Insurance Rate Map (FIRM) Number 08041C0325-F, March 17, 1997.

JPS Engineering, Inc., “Final Drainage Report for Grandview Subdivision,” September 7, 2007(approved by El Paso County 9/14/07).

JPS Engineering, Inc., “Master Development Drainage Plan (MDDP) and Preliminary DrainageReport for Walden Preserve Subdivision,” December 10, 2004 (approved by El Paso County12/20/04).

JPS Engineering, Inc., “Final Drainage Report for Settlers Ranch Subdivision Filing No. 1,”October 18, 2005 (approved by El Paso County 10/19/05).

JPS Engineering, Inc., “Final Drainage Report for Settlers Ranch Subdivision Filing No. 2,” May30, 2008 (approved by El Paso County 3/31/09).

JPS Engineering, Inc., “Final Drainage Report for Walden Pines Subdivision,” March 24, 2004.


JPS Engineering, Inc., “Final Drainage Report for Walden Preserve Subdivision Filing No. 1,” May11, 2005.

II. DRAINAGE BASINS AND SUB-BASINS

A. Major Basin Description

The proposed development lies within both the West Cherry Creek Drainage Basin (CYCY 0400)and East Cherry Creek Drainage Basin (CYCY 0200), as classified by El Paso County. Drainagefrom the west part of the site flows southwesterly to an eastern tributary of West Cherry Creek,which flows to a confluence with the main channel north of Walker Road. Downstreamagricultural areas generally drain northerly towards the main channel of West Cherry Creek.

Drainage from the east part of the site flows easterly to a tributary of East Cherry Creek.

No drainage planning study has been completed for this drainage basin or any adjacent drainagebasins. In the absence of plans for regional drainage facilities, El Paso County generally requiresnew developments to provide stormwater detention to maintain historic runoff flows leavingdeveloped areas.

The major drainage basins lying in and around the proposed development are depicted in FigureEX1. The Settlers View parcel is located near the southerly limits of the West Cherry Creek andEast Cherry Creek Drainage Basins, each of which comprise total drainage areas in excess of 30square miles. As such, the proposed 40-acre Settlers View subdivision represents less than 0.2percent of the total basin area, which is primarily ranch land.

B. Floodplain Impacts

The proposed development area is located beyond the limits of any 100-year floodplaindelineated by the Federal Emergency Management Agency (FEMA). The floodplain limits in thevicinity of the site are shown in Flood Insurance Rate Map (FIRM) Panel Number 08041C0325-F, dated March 17, 1997, as shown in Figure FIRM (Appendix F).

C. Sub-Basin Description

The existing drainage basins lying in and around the proposed development are depicted in FigureEX1 (Appendix F). The existing on-site topography has been delineated as several sub-basinsdraining to design points at the east and west boundaries of the site.

The developed drainage basins lying within the proposed development are depicted on Figure D1.The developed site layout has been divided into sub-basins based on the proposed road layoutwithin the site. The natural drainage patterns will be impacted through development by site gradingand concentration of runoff in subdivision roadside ditches and channels.


On-site flows will be diverted to the existing natural drainage swales and channels running throughthe property, following historic drainage paths.

III. DRAINAGE DESIGN CRITERIA

A. Development Criteria Reference

No Drainage Basin Planning Study (DBPS) has been completed for either the West Cherry CreekDrainage Basin or the East Cherry Creek Drainage Basin. Previous drainage reports for completedsubdivision filings have proposed to provide on-site detention for mitigation of developed flows.

B. Hydrologic Criteria

In accordance with the El Paso County Drainage Criteria Manual, Rational Method procedureswere utilized for hydrologic calculations since the tributary drainage basins are below 100 acres.

Rational Method hydrologic calculations were based on the following assumptions:

Design storm (minor) 5-year Design storm (major) 100-year Time of Concentration – Overland Flow “Airport” equation (300’ max. developed) Time of Concentration – Gutter/Ditch Flow “SCS Upland” equation Rainfall Intensities El Paso County I-D-F Curve Hydrologic soil type B

C5 C100 Runoff Coefficients - undeveloped:

Existing pasture/range areas 0.08 0.35 Runoff Coefficients - developed:

Proposed lot areas (2.5-acre lots) 0.170 0.417

Hydrologic calculations are enclosed in Appendix A, and peak design flows are identified on thedrainage basin drawings.


IV. DRAINAGE PLANNING FOUR STEP PROCESS

El Paso County Drainage Criteria require drainage planning to include a Four Step Process forreceiving water protection that focuses on reducing runoff volumes, treating the water qualitycapture volume (WQCV), stabilizing drainageways, and implementing long-term source controls.As stated in DCM Volume 2, the Four Step Process is applicable to all new and re-development

projects with construction activities that disturb 1 acre or greater or that disturb less than 1 acrebut are part of a larger common plan of development. The Four Step Process has beenimplemented as follows in the planning of this project:

Step 1: Employ Runoff Reduction Practices Minimize Impacts: The proposed rural residential subdivision development with 2.5-acre

minimum lot sizes provides for inherently minimal drainage impacts based on the limitedimpervious areas associated with rural residential development.

Minimize Directly Connected Impervious Areas (MDCIA): The rural residentialdevelopment will have roadside ditches along all roads, providing for impervious areas todrain across pervious areas. Based on the roadside ditches throughout the subdivision,the subdivision is classified as MDCIA Level One.

Grass Swales: The proposed roadside ditches will drain to existing and proposed grass-lined drainage swales following historic drainage patterns through the property.

Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release FSD: A Full-Spectrum Detention Pond will be provided at the west boundary of the site.

On-site drainage will be routed through the extended detention basin, which will captureand slowly release the WQCV over a 72-hour design release period.

Step 3: Stabilize Drainageways Proper erosion control measures will be implemented along the roadside ditches and

grass-lined drainage channels to provide stabilized drainageways within the site.

Step 4: Implement Site Specific and Other Source Control BMPs No industrial or commercial land uses are proposed within this rural residential

subdivision. On-site drainage will be routed through the private Full-Spectrum Detention (FSD) basin

to minimize introduction of contaminants to the County’s public drainage system.

V. DRAINAGE FACILITY DESIGN

A. General Concept

Development of the Settlers View Subdivision will require site grading and paving, resulting inadditional impervious areas across the site. The general drainage pattern will consist of gradingaway from home sites to swales and roadside ditches along the internal roads within the

dsdlaforceText BoxUpdate the 4 step process based on the steps identified in Appendix I Section I.7.2 which are different from the city.


subdivision, conveying runoff flows through the site. Runoff from the site will flow by roadsideditches to cross culverts at low points in the road profiles, and grass-lined channels connecting toexisting natural swales at the site boundaries.

The stormwater management concept for the Settlers View development will be to provideroadside ditches and natural swales as required to convey developed drainage through the site toexisting natural outfalls. Individual lot grading will provide positive drainage away from buildingsites, and direct developed flows into the system of roadside ditches and drainage swales runningthrough the subdivision.

A stormwater detention pond will be constructed at the west boundary of the subdivision tomitigate the impact of developed flows and maintain historic peak flows downstream of theproperty.

B. Specific Details

1. Existing Drainage Conditions

Historic drainage conditions within the site are depicted in Figure EX1. Basin Acomprises the eastern side of the property, which drains easterly along several existingnatural swales. Basin A flows easterly to Design Pont #A, with historic peak flowscalculated as Q5 = 3.0 cfs and Q100 = 21.6 cfs.

Basin A discharges to an existing grass-lined drainage swale flowing easterly across theadjoining 40-acre property to an existing stock pond, ultimately crossing Steppler Road inan existing 48-inch RCP Culvert.

The west side of the property has been delineated as Basin S1, which flows southwesterly toan existing grass-lined drainage swale at the west boundary of the site. Off-site Basin OS1comprises a relatively small area within the adjoining Grandview Subdivision, which flowssouthwesterly into the northwest corner of Basin S1. Additionally, off-site drainage fromBasin D9 of the adjoining Settlers Ranch Subdivision flows northwesterly through BasinS1. Flows from Basins OS1, D9, and S1 combine at Design Pont #S1, with historic peakflows calculated as Q5 = 10.0 cfs and Q100 = 73.1 cfs.

Basin S1 discharges to an existing grass-lined drainage swale flowing westerly across theadjoining 40-acre property to the existing downstream drainage channel and series of pondswithin the Walden Preserve Subdivision.

2. Developed Drainage Conditions

The developed drainage basins and projected flows are shown in Figure D1, and hydrologiccalculations are enclosed in Appendix B.

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dsdlaforceCloud+Figure EX1 labels the basin as "S". Revise accordingly.


The east side of the property has been delineated as Basins A, B, and C in the developedcondition, and these basins will continue to sheet flow easterly through the proposed AbertRanch Subdivision.

Basin A flows easterly to Design Point #A, with developed peak flows calculated asQ5 = 5.5 cfs and Q100 = 22.4 cfs. Basin B flows easterly to Design Point #B, with developedpeak flows calculated as Q5 = 1.7 cfs and Q100 = 6.8 cfs. Basin C flows easterly to DesignPoint #C, with developed peak flows calculated as Q5 = 0.8 cfs and Q100 = 3.1 cfs.Combined developed flows from Basins A, B, and C are calculated as Q5 = 7.6 cfs andQ100 = 31.2 cfs (Design Point #A1).

Development plans for the proposed Abert Ranch Subdivision on the adjoining ranchproperty to the east include upgrade of an existing stock pond to meet stormwater detentionrequirements for the Abert Ranch site, including the minimal developed drainagecontribution from Settlers View Basins A, B, and C.

The west side of the property has been delineated as Basins S1-S4 based on the developedroad configuration, and these basins will continue to flow westerly to the existing drainageswale at the western property boundary.

Developed Basin S1 will flow southwesterly to the proposed Culvert S1 crossing SilverNell Drive at Design Point #S1. Culvert S1 fill flow northwesterly through the existinggrass-lined drainage swale in Basin S3 to a proposed Full-Spectrum Detention Pond (PondS3) at the west boundary of the subdivision.

Off-site drainage from Basin D9 of the adjoining Settlers Ranch Subdivision will flownorthwesterly through Basin S2 to the proposed Culvert S2 crossing Settlers View Road atDesign Point #S2, continuing through a grass-lined channel to Detention Pond S3.

Flows from Basins D9 and S1-S3 combine at Design Point #S3, with developed peak flowsof Q5 = 19.0 cfs and Q100 = 78.1 cfs.

Off-site Basin OS1 will continue to flow northwesterly through Basin S4 to the westboundary of the site.

Flows from Basins D9, OS1, and S1-S4 combine at Design Point #S, with developed peakflows of Q5 = 22.0 cfs and Q100 = 90.6 cfs. Developed flow impacts will be mitigated byrouting flows through Detention Pond #S3.

C. Comparison of Developed to Historic Discharges

Based on the hydrologic calculations in Appendix B, the proposed development will result indeveloped flows exceeding historic flows from the parcel. The increase in developed flows will bemitigated through on-site stormwater detention facilities.

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dsdlaforceCloud+Not shown on Figure D1. Is this DP #S3

dsdlaforceCalloutInconsistent with the next paragraph. Map indicates OS1 & S4 flows do not combine with Basin D9 and S1-S3 upstream of Pond S3.

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The comparison of developed to historic discharges at key design points is summarized as follows:

DesignPoint

Historic Flow Developed Flow Comparison of Developedto Historic Flow

(Q5%/Q100%)Area(ac)

Q5(cfs)

Q100(cfs)

Area(ac)

Q5(cfs)

Q100(cfs)

A 15.0 3.0 21.6 15.0 7.6 31.2 253% / 144% (increase)

S 46.8 10.0 73.1 46.8 22.0 90.6 220% / 124% (increase)

D. Detention Ponds

The Developed storm runoff downstream of the proposed subdivision will be maintained at historiclevels by routing flows through a proposed detention pond at the west boundary of the property.Pond #S3 will be constructed as a Full-Spectrum Detention (FSD) Pond to mitigate developed flowimpacts from the proposed subdivision. The pond outlet structure has been designed with multipleorifice openings to detain the full spectrum of storm events.

Detailed pond routing calculations have been performed utilizing the Denver Urban Drainage “UD-Detention” software package (see Appendix C). The pond outlet structure configuration has beendesigned to maintain the calculated pond discharge below the target outflow, while maintaining themaximum water surface elevation below the pond spillway. Final detention pond designparameters are summarized as follows:

Pond Inflow(Q100, cfs)

Outflow(Q100, cfs)

Volume(ac-ft)

OutletStructure

Pond #S3 78.1 24.2 0.44 24-inch SD w/ multiple orifices

15-foot wide gravel maintenance access roads will be provided for all stormwater detentionfacilities. The proposed detention ponds will be privately owned and maintained by the subdivisionhomeowners association (HOA). An Operation & Maintenance (O&M) Manual for the detentionpond is enclosed in Appendix D.

E. On-Site Drainage Facility Design

Developed sub-basins and proposed drainage improvements are depicted in the enclosed DrainagePlan (Sheet D1). In accordance with El Paso County standards, new roadways will be graded witha minimum longitudinal slope of 1.0 percent. The typical local road section will consist of a 28-foot paved width with 2-foot gravel shoulders and 4:1 slopes to 2.5-foot ditches.

On-site drainage facilities will consist of roadside ditches, grass-lined channels, and culverts.Hydraulic calculations for preliminary sizing of major on-site drainage facilities are enclosed inAppendix D, and design criteria are summarized as follows:


1. Culverts

The internal road system has been graded to drain roadside ditches to low points along theroad profile, where cross-culverts will convey developed flows into grass-lined channelsfollowing historic drainage paths. Culvert pipes have been specified as reinforced concretepipe (RCP) with a minimum diameter of 18-inches. Culvert sizes have been identifiedbased on a maximum headwater-to-depth ratio (HW/D) of 1.0 for the minor (5-year) designstorm. Final culvert design calculations were performed utilizing the FHWA HY-8software package to perform a detailed analysis of inlet and outlet control conditions,meeting El Paso County criteria for allowable overtopping. HY8 calculation results aresummarized in the “Culvert Sizing Summary” Table in Appendix B. Riprap outletprotection will be provided at all culverts.

2. Open Channels

Drainage easements will be dedicated along major drainage channels following historicdrainage paths through the subdivision. These channels will generally be grass-linedchannels designed to convey 100-year flows, with a trapezoidal cross-section, variablebottom width and depth, 4:1 maximum side slopes, 1-foot freeboard, and a minimum slopeof 0.5 percent.

The proposed drainage channels have been sized utilizing Manning’s equation for openchannel flow, assuming a friction factor (“n”) of 0.030 for dry-land grass channels.Maximum allowable velocities will be evaluated based on El Paso County drainage criteria,typically allowing for a maximum 100-year velocity of 5 feet per second. Erosion controlmats have been specified for channel segments with maximum 100-year velocities up to 8feet per second. The proposed channels will generally be seeded with native grasses forerosion control. Erosion control mats, ditch checks, and/or riprap channel lining will beprovided where required based on erosive velocities. Ditch flows will be diverted todrainage channels at the nearest practical location to minimize excessive roadside ditchsizes. Detailed channel hydraulic calculations are enclosed in Appendix B.

Primary drainage swales crossing proposed lots have been placed in drainage easements,with variable widths based on the required channel sections.

F. Anticipated Drainage Problems and Solutions

The proposed stormwater Detention Pond #S3 has been designed to mitigate the impacts ofdeveloped drainage from this project. The overall drainage plan for the subdivision includes asystem of roadside ditches, channels, and culverts to convey developed flows through the site. Theprimary drainage problems anticipated within this development will consist of maintenance of thesedrainage channels, culverts, and detention pond facilities. Care will need to be taken to implementproper erosion control measures in the proposed roadside ditches, channels, and swales.


Ditches will be designed to meet allowable velocity criteria. Erosion control mats, ditch checks,and riprap channel lining will be installed where necessary to minimize erosion concerns. Properconstruction and maintenance of the proposed detention facilities will minimize downstreamdrainage impacts. Public roadway improvements and ditches within the public right-of-way will beowned and maintained by El Paso County. The proposed stormwater detention pond and drainagechannels located within open space tracts will be owned and maintained by the subdivision HOA.

VI. EROSION / SEDIMENT CONTROL

The Contractor will be required to implement Best Management Practices (BMP’s) for erosioncontrol through the course of construction. Sediment control measures will include installationof silt fence at the toe of disturbed slopes and hay bales protecting drainage ditches. Cut slopeswill be stabilized during excavation as necessary and vegetation will be established forstabilization of disturbed areas as soon as possible. All ditches will be designed to meet El PasoCounty criteria for slope and velocity. The proposed detention pond will serve as a sediment basinduring the construction phase of the project.

VII. COST ESTIMATE AND DRAINAGE FEES

A cost estimate for proposed drainage improvements is enclosed in Appendix E, with a totalestimated cost of approximately $42,500 for subdivision drainage improvements. The developerwill finance all construction costs for proposed roadway and drainage improvements, and publicfacilities will be owned and maintained by El Paso County upon final acceptance. Privatedrainage facilities will be owned and maintained by the subdivision HOA. This parcel is locatedin the West Cherry Creek and East Cherry Creek Drainage Basins. No drainage and bridge feeswill be due at time of recordation of the final plat as the subject site is not located in a fee basin.

VIII. SUMMARY

Settlers View is a proposed residential subdivision consisting of 14 lots on a 40-acre parcellocated between Grandview Subdivision and Settlers Ranch Subdivision on the west side ofSteppler Road in northeastern El Paso County. Development of the proposed Settlers ViewSubdivision will generate an increase in developed runoff from the site, which will be mitigatedthrough construction of on-site stormwater detention facilities. The proposed drainage patternswill remain consistent with historic conditions, and new drainage facilities constructed to El PasoCounty standards will safely convey runoff to suitable outfalls. Based on the on-site stormwaterdetention concept, no new downstream drainage facilities are proposed.

The proposed detention pond will ensure that overall developed flows from the Settlers ViewSubdivision remain consistent with historic levels. Construction and proper maintenance of theproposed drainage and erosion control facilities will ensure that this subdivision has nosignificant adverse drainage impact on downstream or surrounding areas.

APPENDIX A

HYDROLOGIC CALCULATIONS

Hydrologic Soil Group—El Paso County Area, Colorado(Settlers View)

Natural ResourcesConservation Service

Web Soil SurveyNational Cooperative Soil Survey

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521960 522050 522140 522230 522320 522410 522500

521960 522050 522140 522230 522320 522410 522500

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Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS840 150 300 600 900

Feet0 50 100 200 300

MetersMap Scale: 1:3,590 if printed on A portrait (8.5" x 11") sheet.

Soil Map may not be valid at this scale.

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Hydrologic Soil Group

Hydrologic Soil Group— Summary by Map Unit — El Paso County Area, Colorado (CO625)

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

25 Elbeth sandy loam, 3 to8 percent slopes

B 3.0 7.2%

67 Peyton sandy loam, 5 to9 percent slopes

B 14.0 33.6%

92 Tomah-Crowfoot loamysands, 3 to 8 percentslopes

B 24.6 59.2%

Totals for Area of Interest 41.6 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils areassigned to one of four groups according to the rate of water infiltration when thesoils are not protected by vegetation, are thoroughly wet, and receiveprecipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) andthree dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) whenthoroughly wet. These consist mainly of deep, well drained to excessivelydrained sands or gravelly sands. These soils have a high rate of watertransmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. Theseconsist chiefly of moderately deep or deep, moderately well drained or welldrained soils that have moderately fine texture to moderately coarse texture.These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consistchiefly of soils having a layer that impedes the downward movement of water orsoils of moderately fine texture or fine texture. These soils have a slow rate ofwater transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) whenthoroughly wet. These consist chiefly of clays that have a high shrink-swellpotential, soils that have a high water table, soils that have a claypan or claylayer at or near the surface, and soils that are shallow over nearly imperviousmaterial. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter isfor drained areas and the second is for undrained areas. Only the soils that intheir natural condition are in group D are assigned to dual classes.

Hydrologic Soil Group—El Paso County Area, Colorado Settlers View



12/23/2016Page 3 of 4

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—El Paso County Area, Colorado Settlers View



12/23/2016Page 4 of 4

United StatesDepartment ofAgriculture

A product of the NationalCooperative Soil Survey,a joint effort of the UnitedStates Department ofAgriculture and otherFederal agencies, Stateagencies including theAgricultural ExperimentStations, and localparticipants

Custom Soil ResourceReport for

El Paso CountyArea, Colorado

NaturalResourcesConservationService

December 23, 2016

PrefaceSoil surveys contain information that affects land use planning in survey areas.They highlight soil limitations that affect various land uses and provide informationabout the properties of the soils in the survey areas. Soil surveys are designed formany different users, including farmers, ranchers, foresters, agronomists, urbanplanners, community officials, engineers, developers, builders, and home buyers.Also, conservationists, teachers, students, and specialists in recreation, wastedisposal, and pollution control can use the surveys to help them understand,protect, or enhance the environment.

Various land use regulations of Federal, State, and local governments may imposespecial restrictions on land use or land treatment. Soil surveys identify soilproperties that are used in making various land use or land treatment decisions.The information is intended to help the land users identify and reduce the effects ofsoil limitations on various land uses. The landowner or user is responsible foridentifying and complying with existing laws and regulations.

Although soil survey information can be used for general farm, local, and wider areaplanning, onsite investigation is needed to supplement this information in somecases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/) and certain conservation and engineeringapplications. For more detailed information, contact your local USDA Service Center(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State SoilScientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?cid=nrcs142p2_053951).

Great differences in soil properties can occur within short distances. Some soils areseasonally wet or subject to flooding. Some are too unstable to be used as afoundation for buildings or roads. Clayey or wet soils are poorly suited to use asseptic tank absorption fields. A high water table makes a soil poorly suited tobasements or underground installations.

The National Cooperative Soil Survey is a joint effort of the United StatesDepartment of Agriculture and other Federal agencies, State agencies including theAgricultural Experiment Stations, and local agencies. The Natural ResourcesConservation Service (NRCS) has leadership for the Federal part of the NationalCooperative Soil Survey.

Information about soils is updated periodically. Updated information is availablethrough the NRCS Web Soil Survey, the site for official soil survey information.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all itsprograms and activities on the basis of race, color, national origin, age, disability,and where applicable, sex, marital status, familial status, parental status, religion,sexual orientation, genetic information, political beliefs, reprisal, or because all or apart of an individual's income is derived from any public assistance program. (Notall prohibited bases apply to all programs.) Persons with disabilities who require

2

alternative means for communication of program information (Braille, large print,audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voiceand TDD). To file a complaint of discrimination, write to USDA, Director, Office ofCivil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 orcall (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunityprovider and employer.

3

ContentsPreface.................................................................................................................... 2How Soil Surveys Are Made..................................................................................5Soil Map.................................................................................................................. 8

Soil Map................................................................................................................9Legend................................................................................................................10Map Unit Legend................................................................................................ 11Map Unit Descriptions.........................................................................................11

El Paso County Area, Colorado...................................................................... 1325—Elbeth sandy loam, 3 to 8 percent slopes............................................1367—Peyton sandy loam, 5 to 9 percent slopes...........................................1492—Tomah-Crowfoot loamy sands, 3 to 8 percent slopes..........................15

References............................................................................................................17

4

How Soil Surveys Are MadeSoil surveys are made to provide information about the soils and miscellaneousareas in a specific area. They include a description of the soils and miscellaneousareas and their location on the landscape and tables that show soil properties andlimitations affecting various uses. Soil scientists observed the steepness, length,and shape of the slopes; the general pattern of drainage; the kinds of crops andnative plants; and the kinds of bedrock. They observed and described many soilprofiles. A soil profile is the sequence of natural layers, or horizons, in a soil. Theprofile extends from the surface down into the unconsolidated material in which thesoil formed or from the surface down to bedrock. The unconsolidated material isdevoid of roots and other living organisms and has not been changed by otherbiological activity.

Currently, soils are mapped according to the boundaries of major land resourceareas (MLRAs). MLRAs are geographically associated land resource units thatshare common characteristics related to physiography, geology, climate, waterresources, soils, biological resources, and land uses (USDA, 2006). Soil surveyareas typically consist of parts of one or more MLRA.

The soils and miscellaneous areas in a survey area occur in an orderly pattern thatis related to the geology, landforms, relief, climate, and natural vegetation of thearea. Each kind of soil and miscellaneous area is associated with a particular kindof landform or with a segment of the landform. By observing the soils andmiscellaneous areas in the survey area and relating their position to specificsegments of the landform, a soil scientist develops a concept, or model, of how theywere formed. Thus, during mapping, this model enables the soil scientist to predictwith a considerable degree of accuracy the kind of soil or miscellaneous area at aspecific location on the landscape.

Commonly, individual soils on the landscape merge into one another as theircharacteristics gradually change. To construct an accurate soil map, however, soilscientists must determine the boundaries between the soils. They can observe onlya limited number of soil profiles. Nevertheless, these observations, supplementedby an understanding of the soil-vegetation-landscape relationship, are sufficient toverify predictions of the kinds of soil in an area and to determine the boundaries.

Soil scientists recorded the characteristics of the soil profiles that they studied. Theynoted soil color, texture, size and shape of soil aggregates, kind and amount of rockfragments, distribution of plant roots, reaction, and other features that enable themto identify soils. After describing the soils in the survey area and determining theirproperties, the soil scientists assigned the soils to taxonomic classes (units).Taxonomic classes are concepts. Each taxonomic class has a set of soilcharacteristics with precisely defined limits. The classes are used as a basis forcomparison to classify soils systematically. Soil taxonomy, the system of taxonomicclassification used in the United States, is based mainly on the kind and characterof soil properties and the arrangement of horizons within the profile. After the soil

5

scientists classified and named the soils in the survey area, they compared theindividual soils with similar soils in the same taxonomic class in other areas so thatthey could confirm data and assemble additional data based on experience andresearch.

The objective of soil mapping is not to delineate pure map unit components; theobjective is to separate the landscape into landforms or landform segments thathave similar use and management requirements. Each map unit is defined by aunique combination of soil components and/or miscellaneous areas in predictableproportions. Some components may be highly contrasting to the other componentsof the map unit. The presence of minor components in a map unit in no waydiminishes the usefulness or accuracy of the data. The delineation of suchlandforms and landform segments on the map provides sufficient information for thedevelopment of resource plans. If intensive use of small areas is planned, onsiteinvestigation is needed to define and locate the soils and miscellaneous areas.

Soil scientists make many field observations in the process of producing a soil map.The frequency of observation is dependent upon several factors, including scale ofmapping, intensity of mapping, design of map units, complexity of the landscape,and experience of the soil scientist. Observations are made to test and refine thesoil-landscape model and predictions and to verify the classification of the soils atspecific locations. Once the soil-landscape model is refined, a significantly smallernumber of measurements of individual soil properties are made and recorded.These measurements may include field measurements, such as those for color,depth to bedrock, and texture, and laboratory measurements, such as those forcontent of sand, silt, clay, salt, and other components. Properties of each soiltypically vary from one point to another across the landscape.

Observations for map unit components are aggregated to develop ranges ofcharacteristics for the components. The aggregated values are presented. Directmeasurements do not exist for every property presented for every map unitcomponent. Values for some properties are estimated from combinations of otherproperties.

While a soil survey is in progress, samples of some of the soils in the area generallyare collected for laboratory analyses and for engineering tests. Soil scientistsinterpret the data from these analyses and tests as well as the field-observedcharacteristics and the soil properties to determine the expected behavior of thesoils under different uses. Interpretations for all of the soils are field tested throughobservation of the soils in different uses and under different levels of management.Some interpretations are modified to fit local conditions, and some newinterpretations are developed to meet local needs. Data are assembled from othersources, such as research information, production records, and field experience ofspecialists. For example, data on crop yields under defined levels of managementare assembled from farm records and from field or plot experiments on the samekinds of soil.

Predictions about soil behavior are based not only on soil properties but also onsuch variables as climate and biological activity. Soil conditions are predictable overlong periods of time, but they are not predictable from year to year. For example,soil scientists can predict with a fairly high degree of accuracy that a given soil willhave a high water table within certain depths in most years, but they cannot predictthat a high water table will always be at a specific level in the soil on a specific date.

After soil scientists located and identified the significant natural bodies of soil in thesurvey area, they drew the boundaries of these bodies on aerial photographs and

Custom Soil Resource Report

6

identified each as a specific map unit. Aerial photographs show trees, buildings,fields, roads, and rivers, all of which help in locating boundaries accurately.


7

Soil MapThe soil map section includes the soil map for the defined area of interest, a list ofsoil map units on the map and extent of each map unit, and cartographic symbolsdisplayed on the map. Also presented are various metadata about data used toproduce the map, and a description of each soil map unit.

8

9

Custom Soil Resource ReportSoil Map

4325

420

4325

510

4325

600

4325

690

4325

780

4325

870

4325

960

4326

050

4326

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4325

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4325

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4325

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4325

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4325

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4325

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521960 522050 522140 522230 522320 522410 522500

521960 522050 522140 522230 522320 522410 522500

39° 5' 3'' N10

4° 4

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39° 5' 3'' N

104°

44'

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39° 4' 39'' N

104°

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39° 4' 39'' N

104°

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' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS840 150 300 600 900

Feet0 50 100 200 300

MetersMap Scale: 1:3,590 if printed on A portrait (8.5" x 11") sheet.

Soil Map may not be valid at this scale.

MA

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10

Map Unit Legend

El Paso County Area, Colorado (CO625)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

25 Elbeth sandy loam, 3 to 8percent slopes

3.0 7.2%

67 Peyton sandy loam, 5 to 9percent slopes

14.0 33.6%

92 Tomah-Crowfoot loamy sands,3 to 8 percent slopes

24.6 59.2%

Totals for Area of Interest 41.6 100.0%

Map Unit DescriptionsThe map units delineated on the detailed soil maps in a soil survey represent thesoils or miscellaneous areas in the survey area. The map unit descriptions, alongwith the maps, can be used to determine the composition and properties of a unit.

A map unit delineation on a soil map represents an area dominated by one or moremajor kinds of soil or miscellaneous areas. A map unit is identified and namedaccording to the taxonomic classification of the dominant soils. Within a taxonomicclass there are precisely defined limits for the properties of the soils. On thelandscape, however, the soils are natural phenomena, and they have thecharacteristic variability of all natural phenomena. Thus, the range of someobserved properties may extend beyond the limits defined for a taxonomic class.Areas of soils of a single taxonomic class rarely, if ever, can be mapped withoutincluding areas of other taxonomic classes. Consequently, every map unit is madeup of the soils or miscellaneous areas for which it is named and some minorcomponents that belong to taxonomic classes other than those of the major soils.

Most minor soils have properties similar to those of the dominant soil or soils in themap unit, and thus they do not affect use and management. These are callednoncontrasting, or similar, components. They may or may not be mentioned in aparticular map unit description. Other minor components, however, have propertiesand behavioral characteristics divergent enough to affect use or to require differentmanagement. These are called contrasting, or dissimilar, components. Theygenerally are in small areas and could not be mapped separately because of thescale used. Some small areas of strongly contrasting soils or miscellaneous areasare identified by a special symbol on the maps. If included in the database for agiven area, the contrasting minor components are identified in the map unitdescriptions along with some characteristics of each. A few areas of minorcomponents may not have been observed, and consequently they are notmentioned in the descriptions, especially where the pattern was so complex that itwas impractical to make enough observations to identify all the soils andmiscellaneous areas on the landscape.

The presence of minor components in a map unit in no way diminishes theusefulness or accuracy of the data. The objective of mapping is not to delineatepure taxonomic classes but rather to separate the landscape into landforms or


11

landform segments that have similar use and management requirements. Thedelineation of such segments on the map provides sufficient information for thedevelopment of resource plans. If intensive use of small areas is planned, however,onsite investigation is needed to define and locate the soils and miscellaneousareas.

An identifying symbol precedes the map unit name in the map unit descriptions.Each description includes general facts about the unit and gives important soilproperties and qualities.

Soils that have profiles that are almost alike make up a soil series. Except fordifferences in texture of the surface layer, all the soils of a series have majorhorizons that are similar in composition, thickness, and arrangement.

Soils of one series can differ in texture of the surface layer, slope, stoniness,salinity, degree of erosion, and other characteristics that affect their use. On thebasis of such differences, a soil series is divided into soil phases. Most of the areasshown on the detailed soil maps are phases of soil series. The name of a soil phasecommonly indicates a feature that affects use or management. For example, Alphasilt loam, 0 to 2 percent slopes, is a phase of the Alpha series.

Some map units are made up of two or more major soils or miscellaneous areas.These map units are complexes, associations, or undifferentiated groups.

A complex consists of two or more soils or miscellaneous areas in such an intricatepattern or in such small areas that they cannot be shown separately on the maps.The pattern and proportion of the soils or miscellaneous areas are somewhat similarin all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.

An association is made up of two or more geographically associated soils ormiscellaneous areas that are shown as one unit on the maps. Because of presentor anticipated uses of the map units in the survey area, it was not consideredpractical or necessary to map the soils or miscellaneous areas separately. Thepattern and relative proportion of the soils or miscellaneous areas are somewhatsimilar. Alpha-Beta association, 0 to 2 percent slopes, is an example.

An undifferentiated group is made up of two or more soils or miscellaneous areasthat could be mapped individually but are mapped as one unit because similarinterpretations can be made for use and management. The pattern and proportionof the soils or miscellaneous areas in a mapped area are not uniform. An area canbe made up of only one of the major soils or miscellaneous areas, or it can be madeup of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.

Some surveys include miscellaneous areas. Such areas have little or no soilmaterial and support little or no vegetation. Rock outcrop is an example.


12

El Paso County Area, Colorado

25—Elbeth sandy loam, 3 to 8 percent slopes

Map Unit SettingNational map unit symbol: 367xElevation: 7,300 to 7,600 feetFarmland classification: Not prime farmland

Map Unit CompositionElbeth and similar soils: 85 percentEstimates are based on observations, descriptions, and transects of the mapunit.

Description of Elbeth

SettingLandform: HillsLandform position (three-dimensional): Side slopeDown-slope shape: LinearAcross-slope shape: LinearParent material: Alluvium derived from arkose

Typical profileA - 0 to 3 inches: sandy loamE - 3 to 23 inches: loamy sandBt - 23 to 68 inches: sandy clay loamC - 68 to 74 inches: sandy clay loam

Properties and qualitiesSlope: 3 to 8 percentDepth to restrictive feature: More than 80 inchesNatural drainage class: Well drainedRunoff class: MediumCapacity of the most limiting layer to transmit water (Ksat): Moderately high (0.20

to 0.60 in/hr)Depth to water table: More than 80 inchesFrequency of flooding: NoneFrequency of ponding: NoneAvailable water storage in profile: Moderate (about 7.1 inches)

Interpretive groupsLand capability classification (irrigated): None specifiedLand capability classification (nonirrigated): 4eHydrologic Soil Group: BHydric soil rating: No

Minor Components

Other soilsPercent of map unit: Hydric soil rating: No


13

67—Peyton sandy loam, 5 to 9 percent slopes

Map Unit SettingNational map unit symbol: 369dElevation: 6,800 to 7,600 feetMean annual air temperature: 43 to 45 degrees FFrost-free period: 115 to 125 daysFarmland classification: Not prime farmland

Map Unit CompositionPeyton and similar soils: 85 percentEstimates are based on observations, descriptions, and transects of the mapunit.

Description of Peyton

SettingLandform: HillsLandform position (three-dimensional): Side slopeDown-slope shape: LinearAcross-slope shape: LinearParent material: Arkosic alluvium derived from sedimentary rock and/or arkosic

residuum weathered from sedimentary rock

Typical profileA - 0 to 12 inches: sandy loamBt - 12 to 25 inches: sandy clay loamBC - 25 to 35 inches: sandy loamC - 35 to 60 inches: sandy loam

Properties and qualitiesSlope: 5 to 9 percentDepth to restrictive feature: More than 80 inchesNatural drainage class: Well drainedRunoff class: MediumCapacity of the most limiting layer to transmit water (Ksat): Moderately high (0.20

to 0.60 in/hr)Depth to water table: More than 80 inchesFrequency of flooding: NoneFrequency of ponding: NoneAvailable water storage in profile: Moderate (about 7.3 inches)

Interpretive groupsLand capability classification (irrigated): None specifiedLand capability classification (nonirrigated): 4eHydrologic Soil Group: BEcological site: Sandy Divide (R049BY216CO)Hydric soil rating: No


14

Minor Components


PleasantPercent of map unit: Landform: DepressionsHydric soil rating: Yes

92—Tomah-Crowfoot loamy sands, 3 to 8 percent slopes

Map Unit SettingNational map unit symbol: 36b9Elevation: 7,300 to 7,600 feetFarmland classification: Not prime farmland

Map Unit CompositionTomah and similar soils: 50 percentCrowfoot and similar soils: 30 percentEstimates are based on observations, descriptions, and transects of the mapunit.

Description of Tomah

SettingLandform: Alluvial fans, hillsLandform position (three-dimensional): Side slope, crestDown-slope shape: LinearAcross-slope shape: LinearParent material: Alluvium derived from arkose and/or residuum weathered from

arkose

Typical profileA - 0 to 10 inches: loamy sandE - 10 to 22 inches: coarse sandC - 48 to 60 inches: coarse sand

Properties and qualitiesSlope: 3 to 8 percentDepth to restrictive feature: More than 80 inchesNatural drainage class: Well drainedRunoff class: MediumCapacity of the most limiting layer to transmit water (Ksat): Moderately high to

high (0.60 to 2.00 in/hr)Depth to water table: More than 80 inchesFrequency of flooding: NoneFrequency of ponding: NoneAvailable water storage in profile: Very low (about 2.0 inches)


15


Description of Crowfoot

SettingLandform: Alluvial fans, hillsLandform position (three-dimensional): Side slope, crestDown-slope shape: LinearAcross-slope shape: LinearParent material: Alluvium

Typical profileA - 0 to 12 inches: loamy sandE - 12 to 23 inches: sandBt - 23 to 36 inches: sandy clay loamC - 36 to 60 inches: coarse sand

Properties and qualitiesSlope: 3 to 8 percentDepth to restrictive feature: More than 80 inchesNatural drainage class: Well drainedRunoff class: MediumCapacity of the most limiting layer to transmit water (Ksat): Moderately high to

high (0.60 to 2.00 in/hr)Depth to water table: More than 80 inchesFrequency of flooding: NoneFrequency of ponding: NoneAvailable water storage in profile: Low (about 4.7 inches)


Minor Components


PleasantPercent of map unit: Landform: DepressionsHydric soil rating: Yes


16

ReferencesAmerican Association of State Highway and Transportation Officials (AASHTO).2004. Standard specifications for transportation materials and methods of samplingand testing. 24th edition.

American Society for Testing and Materials (ASTM). 2005. Standard classification ofsoils for engineering purposes. ASTM Standard D2487-00.

Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification ofwetlands and deep-water habitats of the United States. U.S. Fish and WildlifeService FWS/OBS-79/31.

Federal Register. July 13, 1994. Changes in hydric soils of the United States.

Federal Register. September 18, 2002. Hydric soils of the United States.

Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydricsoils in the United States.

National Research Council. 1995. Wetlands: Characteristics and boundaries.

Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service.U.S. Department of Agriculture Handbook 18. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_054262

Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification formaking and interpreting soil surveys. 2nd edition. Natural Resources ConservationService, U.S. Department of Agriculture Handbook 436. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053577

Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department ofAgriculture, Natural Resources Conservation Service. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053580

Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service andDelaware Department of Natural Resources and Environmental Control, WetlandsSection.

United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps ofEngineers wetlands delineation manual. Waterways Experiment Station TechnicalReport Y-87-1.

United States Department of Agriculture, Natural Resources Conservation Service.National forestry manual. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/home/?cid=nrcs142p2_053374

United States Department of Agriculture, Natural Resources Conservation Service.National range and pasture handbook. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/landuse/rangepasture/?cid=stelprdb1043084

17

United States Department of Agriculture, Natural Resources Conservation Service.National soil survey handbook, title 430-VI. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/scientists/?cid=nrcs142p2_054242

United States Department of Agriculture, Natural Resources Conservation Service.2006. Land resource regions and major land resource areas of the United States,the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook296. http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/soils/?cid=nrcs142p2_053624

United States Department of Agriculture, Soil Conservation Service. 1961. Landcapability classification. U.S. Department of Agriculture Handbook 210. http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf


18

Chapter 6 Hydrology

May 2014 City of Colorado Springs 6-17Drainage Criteria Manual, Volume 1

Table 6-6. Runoff Coefficients for Rational Method(Source: UDFCD 2001)

3.2 Time of Concentration

One of the basic assumptions underlying the Rational Method is that runoff is a function of the averagerainfall rate during the time required for water to flow from the hydraulically most remote part of thedrainage area under consideration to the design point. However, in practice, the time of concentration canbe an empirical value that results in reasonable and acceptable peak flow calculations.

For urban areas, the time of concentration (tc) consists of an initial time or overland flow time (ti) plus thetravel time (tt) in the storm sewer, paved gutter, roadside drainage ditch, or drainage channel. For non-urban areas, the time of concentration consists of an overland flow time (ti) plus the time of travel in aconcentrated form, such as a swale or drainageway. The travel portion (tt) of the time of concentrationcan be estimated from the hydraulic properties of the storm sewer, gutter, swale, ditch, or drainageway.Initial time, on the other hand, will vary with surface slope, depression storage, surface cover, antecedentrainfall, and infiltration capacity of the soil, as well as distance of surface flow. The time of concentrationis represented by Equation 6-7 for both urban and non-urban areas.

HSG A&B HSG C&D HSG A&B HSG C&D HSG A&B HSG C&D HSG A&B HSG C&D HSG A&B HSG C&D HSG A&B HSG C&DBusiness Commercial Areas 95 0.79 0.80 0.81 0.82 0.83 0.84 0.85 0.87 0.87 0.88 0.88 0.89 Neighborhood Areas 70 0.45 0.49 0.49 0.53 0.53 0.57 0.58 0.62 0.60 0.65 0.62 0.68

Residential 1/8 Acre or less 65 0.41 0.45 0.45 0.49 0.49 0.54 0.54 0.59 0.57 0.62 0.59 0.65 1/4 Acre 40 0.23 0.28 0.30 0.35 0.36 0.42 0.42 0.50 0.46 0.54 0.50 0.58 1/3 Acre 30 0.18 0.22 0.25 0.30 0.32 0.38 0.39 0.47 0.43 0.52 0.47 0.57 1/2 Acre 25 0.15 0.20 0.22 0.28 0.30 0.36 0.37 0.46 0.41 0.51 0.46 0.56 1 Acre 20 0.12 0.17 0.20 0.26 0.27 0.34 0.35 0.44 0.40 0.50 0.44 0.55

Industrial Light Areas 80 0.57 0.60 0.59 0.63 0.63 0.66 0.66 0.70 0.68 0.72 0.70 0.74 Heavy Areas 90 0.71 0.73 0.73 0.75 0.75 0.77 0.78 0.80 0.80 0.82 0.81 0.83

Parks and Cemeteries 7 0.05 0.09 0.12 0.19 0.20 0.29 0.30 0.40 0.34 0.46 0.39 0.52Playgrounds 13 0.07 0.13 0.16 0.23 0.24 0.31 0.32 0.42 0.37 0.48 0.41 0.54Railroad Yard Areas 40 0.23 0.28 0.30 0.35 0.36 0.42 0.42 0.50 0.46 0.54 0.50 0.58

Undeveloped Areas Historic Flow Analysis-- Greenbelts, Agriculture

20.03 0.05 0.09 0.16 0.17 0.26 0.26 0.38 0.31 0.45 0.36 0.51

Pasture/Meadow 0 0.02 0.04 0.08 0.15 0.15 0.25 0.25 0.37 0.30 0.44 0.35 0.50 Forest 0 0.02 0.04 0.08 0.15 0.15 0.25 0.25 0.37 0.30 0.44 0.35 0.50 Exposed Rock 100 0.89 0.89 0.90 0.90 0.92 0.92 0.94 0.94 0.95 0.95 0.96 0.96 Offsite Flow Analysis (when landuse is undefined)

450.26 0.31 0.32 0.37 0.38 0.44 0.44 0.51 0.48 0.55 0.51 0.59

Streets Paved 100 0.89 0.89 0.90 0.90 0.92 0.92 0.94 0.94 0.95 0.95 0.96 0.96 Gravel 80 0.57 0.60 0.59 0.63 0.63 0.66 0.66 0.70 0.68 0.72 0.70 0.74

Drive and Walks 100 0.89 0.89 0.90 0.90 0.92 0.92 0.94 0.94 0.95 0.95 0.96 0.96Roofs 90 0.71 0.73 0.73 0.75 0.75 0.77 0.78 0.80 0.80 0.82 0.81 0.83Lawns 0 0.02 0.04 0.08 0.15 0.15 0.25 0.25 0.37 0.30 0.44 0.35 0.50

Land Use or SurfaceCharacteristics

PercentImpervious

Runoff Coefficients

2-year 5-year 10-year 25-year 50-year 100-year

Hydrology Chapter 6

6-18 City of Colorado Springs May 2014Drainage Criteria Manual, Volume 1

tic ttt (Eq. 6-7)

Where:

tc = time of concentration (min)

ti = overland (initial) flow time (min)

tt = travel time in the ditch, channel, gutter, storm sewer, etc. (min)

3.2.1 Overland (Initial) Flow Time

The overland flow time, ti, may be calculated using Equation 6-8.

33.05

i (Eq. 6-8)

Where:

ti = overland (initial) flow time (min)C5 = runoff coefficient for 5-year frequency (see Table 6-6)L = length of overland flow (300 ft maximum for non-urban land uses, 100 ft maximum for

urban land uses)S = average basin slope (ft/ft)

Note that in some urban watersheds, the overland flow time may be very small because flows quicklyconcentrate and channelize.

3.2.2 Travel Time

For catchments with overland and channelized flow, the time of concentration needs to be considered incombination with the travel time, tt, which is calculated using the hydraulic properties of the swale, ditch,or channel. For preliminary work, the overland travel time, tt, can be estimated with the help of Figure 6-25 or Equation 6-9 (Guo 1999).

5.0wv (Eq. 6-9)

Where:

V = velocity (ft/s)

Cv = conveyance coefficient (from Table 6-7)

Sw = watercourse slope (ft/ft)

Chapter 6 Hydrology

May 2014 City of Colorado Springs 6-19Drainage Criteria Manual, Volume 1

Table 6-7. Conveyance Coefficient, Cv

Type of Land Surface CvHeavy meadow 2.5

Tillage/field 5

Riprap (not buried)* 6.5

Short pasture and lawns 7

Nearly bare ground 10

Grassed waterway 15

Paved areas and shallow paved swales 20* For buried riprap, select Cv value based on type of vegetative cover.

The travel time is calculated by dividing the flow distance (in feet) by the velocity calculated usingEquation 6-9 and converting units to minutes.

The time of concentration (tc) is then the sum of the overland flow time (ti) and the travel time (tt) perEquation 6-7.

3.2.3 First Design Point Time of Concentration in Urban Catchments

Using this procedure, the time of concentration at the first design point (typically the first inlet in thesystem) in an urbanized catchment should not exceed the time of concentration calculated using Equation6-10. The first design point is defined as the point where runoff first enters the storm sewer system.

(Eq. 6-10)

Where:

tc = maximum time of concentration at the first design point in an urban watershed (min)

L = waterway length (ft)

Equation 6-10 was developed using the rainfall-runoff data collected in the Denver region and, in essence,the Rational Method. Normally, Equation 6-10 will result in a lesser

time of concentration at the first design point and will govern in an urbanized watershed. For subsequentdesign points, the time of concentration is calculated by accumulating the travel times in downstreamdrainageway reaches.

3.2.4 Minimum Time of Concentration

If the calculations result in a tc of less than 10 minutes for undeveloped conditions, it is recommended thata minimum value of 10 minutes be used. The minimum tc for urbanized areas is 5 minutes.

3.2.5 Post-Development Time of Concentration

As Equation 6-8 indicates, the time of concentration is a function of the 5-year runoff coefficient for adrainage basin. Typically, higher levels of imperviousness (higher 5-year runoff coefficients) correspondto shorter times of concentration, and lower levels of imperviousness correspond to longer times of

Hydrology Chapter 6

6-52 City of Colorado Springs May 2014Drainage Criteria Manual, Volume 1

Figure 6-5. Colorado Springs Rainfall Intensity Duration Frequency

IDF Equations

I100 = -2.52 ln(D) + 12.735

I50 = -2.25 ln(D) + 11.375

I25 = -2.00 ln(D) + 10.111

I10 = -1.75 ln(D) + 8.847

I5 = -1.50 ln(D) + 7.583

I2 = -1.19 ln(D) + 6.035

Note: Values calculated byequations may not preciselyduplicate values read from figure.

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final drainage report for settlers view …...final drainage report for settlers view subdivision...

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